1. Field of the Invention
The present invention relates to a structure of a bumper of a vehicle and, more particularly, pertains to a structure of a vehicle bumper whose bumper reinforcement is provided with a plate member having plural openings and plural bead portions formed therein.
2. Description of the Related Art
A conventional bumper structure of a vehicle includes a bumper reinforcement which is mounted between front or rear ends of left and right body frame members, that is, front ends of left and right front side frame members in the case of a front bumper, rear ends of left and right rear side frame members in the case of a rear bumper. The bumper reinforcement includes a beam member extending widthwise across the vehicle body, the beam member having a C-shaped cross section, and a plate member extending widthwise and closing off an open end of the beam member, wherein the beam member and the plate member are united with upper ends of both members joined to each other as are lower ends of both members. As an example, Japanese Unexamined Patent Publication No. 2002-274297 describes this kind of conventional bumper structure.
In the bumper reinforcement thus structured, the beam member and the plate member together form a closed cross section, or a box section, which serves to provide increased strength and stiffness. The box section structure is intended to prevent the bumper reinforcement from becoming unnecessarily collapsed when subjected to an impact load in the event of a vehicle collision. This conventional structure makes it possible to transmit the impact load to a vehicle body frame through a so-called crush can to thereby provide a desired level of energy-absorbing performance.
There is a growing need today for reducing the weight of the bumper reinforcement to help achieve a further reduction in vehicle body weight. In the aforementioned vehicle bumper structure employing the bumper reinforcement provided with the beam member and the plate member which are joined together to form a box section, however, there is a problem that this structure does not allow for a reduction in the vehicle body weight although the structure provides increased strength and stiffness.
One approach that makes possible a reduction in weight of the bumper reinforcement would be to make a plurality of openings in the bumper reinforcement. This approach however develops a problem that a loss of strength and stiffness of the bumper reinforcement will result.